Many of the devices we come to depend on today are battery powered: cell phones, tablets, mp3 players, etc. These typically have a battery power supply that can be recharged, and can typically be recharged from either an AC power source using an adapter or a powered USB port for charging the battery power supply. Conventional devices of this type typically require a +5 volt DC source for charging the battery power supply.
A common issue facing all battery powered devices is they need to re-charge—sometimes when a suitable charging port is not available. To this end, there have been a number of auxiliary supplies sold that consist of a battery source that, when connected to a cell phone, provide extended operation.
Batteries do not, by their nature, provide a consistent voltage at the anode. For example, an alkaline battery might start at 1.6 volts when purchased, but will fade to about 0.9 volts when it is determined depleted. This means that any 5 volt supply generated from a set of four such batteries would benefit from having an internal voltage booster capable of compensating for a drifting supply in order to prolong the interval between recharging of the batteries (in the case of rechargeable batteries) or replacement of the batteries (in the case of disposable batteries).
Most backup supplies of the type discussed above that are sold on the market come equipped with a switch for activating their internal voltage booster. This internal voltage booster requires additional power for operation. Even with no load, an auxiliary power supply is susceptible to self-discharge. The user must remember to turn off the unit when disconnecting a load. Failure to do so means the auxiliary power source may not be available when needed in the future.
An example of a prior art device of the type described above is a Duracell Instant USB charger for cell phones. Booster circuitry within this charger draws current whether powering an external load or whether powering nothing. It is like the electronics in a typical PC computer—it consumes power whether the PC computer is in use or whether the user has left the room and the PC computer sits idle.